The present invention relates to a rotor balancing system for turbomachinery which safely secures balancing rings to a rotor element while reducing windage effects caused by locating slots on the rotor element and to a method for positioning a balancing ring on a rotor element.
In rotating machinery, it sometimes becomes necessary to trim the balance of one of the rotor elements after the machinery has been initially balanced for assembly and has been operating in service. Typically, the machinery must be disassembled, completely or partially, to permit rebalancing or trim balancing of the offending rotor element. With aircraft gas turbine engines, it is desirable to be able to quickly and easily trim balance a compressor rotor after an airfoil has suffered foreign object damage and the damaged blade or blades have been blended in without removal of the engine from an aircraft.
It is known in the prior art to provide a construction for trim balancing a rotating piece of machinery which construction includes an annular rotor element having an outer face and an inner circumference, locating slots around the inner circumference of the rotor element, at least one annular groove within the rotor element behind the rotor element face, balance ring means positioned in the at least one annular groove, which balance ring means is split and has a weighted mass at one end thereof, and tab means connected by pin means to the balance ring means at the weighted mass end, which pin means extends through the rotor element locating slots, and the tab means being mounted on the pin means so as to be external of the rotor element. The construction also includes a casing structure means associated with the rotor element, which casing structure means has an opening therein through which tool means may be inserted to contact the tab means and deflect the pin means inward a controlled distance to free the pin means from the locating slots and permit a circumferential relocating of the balance ring means. Such a trim balancing construction is illustrated in U.S. Pat. No. 5,167,167 to Tiernan, Jr. et al.
One of the deficiencies of the Tiernan, Jr. et al. construction is that the locating slots act similar to rotating blades, turning and heating up the air in the cavities as the rotor element rotates. As a result, heated air is injected into the flow path. The mixture of hot cavity air and cooler flow path air reduces the overall fan efficiency. Additionally, the air pumping (windage) caused by the locating slots forces more air into the flow path. The air impinges with engine core flow reducing overall engine air flow. In addition the locating pin increases windage since it protrudes outboard of the balance ring and acts as a paddle turning air. Subsequently, this adds to the reduction in engine air flow.
Another deficiency in the present design is the ability to fine tune adjust the rotor trim balance. The anti-rotation pin slop and large disk engagement slot decrease the trim balance fine tune adjustment.
Accordingly, it is an object of the present invention to provide a rotor balancing system which reduces windage effects caused by rotor element components.
It is a further object of the present invention to provide a rotor balancing system as above having at least one counterweight balancing ring which substantially eliminates air cavity pumping (windage) caused by locating slots machined into a turbomachinery rotor.
It is a further object of the present invention to provide a rotor balancing system as above which has an integral structure for securing the counterweight balancing rings to the rotor element.
It is yet another object of the present invention to provide an improved method for positioning a counterweight balancing ring on a rotor element.
The foregoing objects are achieved by the rotor balancing system and the method of the present invention.
In accordance with the present invention, a rotor balancing system for turbomachinery comprises a rotor element having a row of locating slots and means for reducing windage effects caused by the locating slots. The windage reducing means comprises at least one balancing ring secured to the rotor element which at least partially covers said locating slots to reduce windage effects.
In another aspect of the present invention, each balancing ring is provided with anti-rotation means for securing it to the rotor element. The anti-rotation means in a preferred construction comprises two integrally formed anti-rotation members for engaging two locating slots on the rotor element.
In yet another aspect of the present invention, each balancing ring is provided with a slot machined into its weighted end. When a tool is placed in the slot and pushed radially inboard, the balancing ring can have its anti-rotation members disengaged from the locating slots and can be rotated to a new position.
In still another aspect of the present invention, a method for positioning a balancing ring on a rotor element is provided. The method comprises providing a rotor element having a row of locating slots and at least one interior annular groove, inserting into the at least one interior annular groove at least one split balancing ring having a weighted end, a slot machined into the weighted end, and means for engaging the locating slots in the rotor element, and inserting the tool into the slot in the weighted end of the at least one balancing ring to disengage the at least one balancing ring from the rotor element and rotate the at least one balancing ring to a balance position.
The rotor balancing system of the present invention adds more disk engagement slots on the disk and an integral anti-rotation pin design sized closely to the disk slot. The result is more capability for fine tuning the trim balance.